This invention relates to polymer blends having a molecular weight distribution (MWD) of at least about 2. In one aspect, the invention relates to ethylene/xcex1-olefin and ethylene/xcex1-olefin/diene monomer polymer blends, particularly blends useful as elastomers, while in another aspect, the invention relates to a process of preparing such blends in a single reactor. In yet another aspect, the invention relates to a process of making the polymer blends in a single reactor using a mixed constrained geometry catalyst (CGC) system.
Constrained geometry catalysts have found wide acceptance in the manufacture of various olefinic polymers, such as the various ethylene, propylene and diene polymers. These catalysts comprise a metal coordination complex which itself comprises a metal of group 4 of the Periodic Table of the Elements and a delocalized xcfx80-bonded moiety substituted with a constrain-inducing moiety, the complex having a constrained geometry about the metal atom such that the angle at the metal between the centroid of the delocalized, substituted xcfx80-bonded moiety and the center of at least one remaining substituent is less than such angle in a similar complex containing a similar xcfx80-bonded moiety lacking in such constrain-inducing substituent. The catalyst further comprises a cocatalyst and an activator. xe2x80x9cDelocalized xcfx80-bonded moietyxe2x80x9d means an unsaturated organic moiety, such as those comprising ethylenic or acetylenic functionality, in which the xcfx80-electrons are donated to the metal to form a bond.
The metal atom is the active site of each discreet CGC unit and since each such unit has a single metal atom, these catalysts tend to produce in a highly efficient manner high molecular weight (e.g., greater than about 10,000 weight average molecular weight) olefin polymers with a narrow MWD (e.g., about 2 or less) over a wide range of polymerization conditions. CGCs are especially useful for the formation of ethylene homopolymers, copolymers of ethylene and one or more xcex1-olefins (i.e., olefins having three or more carbon atoms with the ethylenic unsaturation between the first and second carbon atoms), and interpolymers of ethylene, propylene and a diene monomer (e.g., EPDM terpolymers).
While a narrow MWD can impart useful properties to ethylene-based polymers for certain applications, e.g., transparency in films, ethylene-based polymers with a broad MWD (e.g., greater than about 2) usually process more efficiently and have better physical properties, e.g., temperature performance, for such applications as injection molded or extruded articles, e.g., gaskets and wire and cable coatings, than do ethylene-based polymers with a narrow MWD. Various processes are known for producing broad MWD ethylene-based polymers or polymer blends with a CGC, but all are subject to improvement.
For example, one process for producing such polymers or polymer blends requires the use of multiple reactors deployed in parallel with each reactor containing the same CGC but operated under different polymerization conditions. The product outputs of the reactors are then blended with one another. This produces a polymer blend with a substantially uniform molecular architecture, which is often a desirable property, particularly for elastomers (i.e., polymers with a crystallinity of less than about 45%). For polymer blends of similar crystallinity, those blends of substantially uniform molecular architecture generally exhibit superior physical performance properties, e.g., tensile, modulus, tear, etc., than those blends of a relatively nonuniform molecular architecture. xe2x80x9cSubstantially uniform molecular architecturexe2x80x9d means that each polymer molecule of the blend has substantially the same comonomer content and distribution although the polymer molecules from one reactor differ in weight average molecular weight (Mw) from the polymer molecules produced in the other reactor(s).
One difficulty with this process is that it requires balancing the operation and output of one reactor with the other reactor(s). Another difficulty is that it requires a separate, post-reaction blending step. Yet another difficulty is that with the use of multiple reactors, the ratio of high molecular weight (Mw) to low Mw components in the polymer blend is limited to the capacity of each reactor.
In another process, multiple reactors are deployed in series with each reactor operated at substantially the same polymerization conditions but with each reactor containing a different CGC. The output of the first reactor becomes, of course, a feed for the second reactor, and the product output of the second reactor is a polymer blend. While this process avoids the need for a post-reaction blending step, it still requires balancing the operation of one reactor with the other reactor(s) in the series, and the output of the process is limited by the capacity of the reactors. Moreover, this process often produces a blend in which the molecular architecture is not uniform.
Variations on both of these multiple reactor processes are known, e.g., operating the multiple reactors deployed in series at dissimilar conditions, using a catalyst other than or in addition to a CGC, etc., and U.S. Pat. No. 5,844,045 to Kolthammer and Cardwell, which is incorporated herein by reference, provides a representative description of a multiple reactor process. However, producing a polymer blend in a single reactor, i.e., a reactor blend, saves all the costs associated with running multiple reactors. Moreover, the ratio of high molecular weight (Mw) to low Mw components in the polymer blend can be controlled by controlling the weight ratio of one catalyst to another, and thus the capacity of the individual reactors is not a constraining consideration with respect to this property.
For example, U.S. Pat. No. 4,937,299 to Ewen and Welborn teaches a process for producing (co)polyolefin reactor blends comprising polyethylene and copolyethylene-xcex1-olefins. These blends are prepared in a single reactor by simultaneously polymerizing ethylene and copolymerizing ethylene and an xcex1-olefin in the presence of at least two different metallocenes and an alumoxane. However, Ewen and Welborn do not teach (i) the use of mixed CGC catalyst systems, or (ii) producing an ethylene-based polymer blend having an MWD (a) of at least about 2, and (b) at least ten percent greater than either ethylene-based polymer component of the blend prepared in a single reactor with any single component of the mixed catalyst system under similar polymerization conditions. Ewen and Welborn also do not teach the production of an ethylene-based polymer blend in which each polymer component of the blend has a uniform molecular architecture (at least with respect to the polymer units derived from ethylene and the xcex1-olefin).
U.S. Pat. No. 5,359,015 to Jejelowo teaches a process of producing polyolefins having a controllable broaden MWD utilizing transition metal metallocene catalyst systems comprising a first component comprising at least one transition metal metallocene having at least one cyclopentadienyl ring that is substituted with a first substituent having a secondary or tertiary carbon atom through which it is covalently bonded to the at least on cyclopentadienyl ring in the system, a second component comprising at least one transition metal metallocene having at least one cyclopentadienyl ring that is substituted with a second substituent that is hydrogen or optionally a second hydrocarbon substituent different from the first substituent, and an activator selected from ionic activators or alumoxane or a combination of the two. The MWD of the polymer produced by the catalyst system is generally somewhere between the high and low MWD that such catalyst system components would produce if utilized alone.
U.S. Pat. No. 5,627,117 to Mukaiyama and Oouchi teaches a process for producing a polyolefin with a wide MWD, the process employing an olefin polymerization catalyst comprising a transition metal compound having at least two transition metals in which at least one of the metals is bonded to a ligand having a cyclopentadienyl skeleton at least one of the metals is Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W and lanthanoid metals and the other is a selected transition metal.
WO 93/13143 to Parikh, Cardwell and Kolthammer teaches a process of producing an interpolymer product comprising a first homogeneous ethylene/(xcex1-olefin interpolymer and at least one-second ethylene/xcex1-olefin interpolymer. The process comprises the step of using at least two CGCs having different reactivities such that the first ethylene/xcex1-olefin interpolymer has a narrow MWD with a very high comonomer content and a high molecular weight and the second ethylene/xcex1-olefin interpolymer also has a narrow MWD but a low comonomer content and a molecular weight lower than that of the first interpolymer. The first and second ethylene/xcex1-olefin interpolymers can be polymerized in a single reactor.
WO 99/31147 to Nemzek, Karol and Kao teaches a gas phase ethylene polymerization process which uses a mixed catalyst system comprising at least one supported and at least one unsupported metallocene catalyst. The metallocene catalysts include CGCs, the polymerization process can be conducted in a single reaction vessel, and the process produces a polymer blend. However, none of the polymer blends reported in the examples have an MWD greater than any of the polymer components of the blend, and the molecular architecture of the blend polymer components is unreported.
None of these references, the U.S. patents of which are incorporated herein by reference, however, teach the use of a mixed CGC system to produce a reactor blend (i) having an MWD (a) of at least about 2, and (b) at least ten percent greater than either ethylene-based polymer component of the blend prepared in a single reactor with any single component of the mixed catalyst system under similar polymerization conditions, and (ii) in which each polymer component of the blend has a uniform molecular architecture (at least with respect to the polymer units derived from ethylene and the xcex1-olefin).
According to one embodiment of this invention, an ethylene-based polymer blend (i) having an MWD (a) of at least about 2, and (b) at least ten percent greater than any ethylene-based polymer component of the blend prepared in a single reactor with any single component of the mixed catalyst system under similar polymerization conditions, and (ii) in which each polymer component of the blend has a uniform molecular architecture (at least with respect to the polymer units derived from ethylene and the xcex1-olefin) is prepared by contacting under polymerization conditions and in a single reaction vessel:
A. ethylene,
B. at least one C3-C20 xcex1-olefin, and
C. a mixed CGC system comprising a first catalyst and a second catalyst, each catalyst having substantially the same reactivity ratio and each catalyst comprising:
1. A metal complex of formula I
ZLMXpXxe2x80x2qxe2x80x83xe2x80x83(I)
xe2x80x83wherein
M is a metal of Group 4 of the Periodic Table of the Elements having an oxidation state of +2, +3 or +4 bound in an xcfx805 bonding mode to L;
L is a cyclopentadienyl-, indenyl-, tetrahydroindenyl-, fluorenyl-, tetrahydrofluorenyl-, or octahydrofluorenyl-group covalently substituted with at least the divalent moiety, Z, and L further may be substituted with from 1 to 8 substituents independently selected from the group consisting of hydrocarbyl, halo, halohydrocarbyl, hydrocarbyloxy, dihydrocarbylamine, dihydrocarbylphosphino or silyl groups containing up to 20 nonhydrogen atoms;
Z is a divalent moiety, or a moiety comprising one "sgr"-bond and a neutral two electron pair able to form a coordinate-covalent bond to M, Z comprising boron, or a member of Group 14 of the Periodic Table of the Elements, and also comprising nitrogen, phosphorus, sulfur or oxygen;
X is an anionic ligand group having up to 60 atoms exclusive of the class of ligands that are cyclic, delocalized, xcfx80-bound ligand groups;
Xxe2x80x2 independently each occurrence is a neutral ligating compound having up to 20 atoms;
p is 0, 1 or 2, and is two less than the formal oxidation state of M, with the proviso that when X is a dianionic ligand group, p is 1; and
q is 0, 1 or 2; and
2. An activating cocatalyst;
with the provisos that (i) the first catalyst is different from the second catalyst, (ii) the first catalyst has a reactivity ratio that is substantially the same as the reactivity ratio of the second catalyst with respect to ethylene and the at least one C3-C20 xcex1-olefin, and (iii) the weight ratio of the first catalyst to the second catalyst, based on the weight of the metal M in each catalyst, is between about 90:10 and 10:90.
In another embodiment of the invention, an ethylene-based polymer blend having an MWD (a) of at least about 2, and (b) at least ten percent greater than any ethylene-based polymer component of the blend prepared in a single reactor with any single component of the mixed catalyst system under similar polymerization conditions is prepared by contacting under polymerization conditions and in a single reaction vessel:
A. ethylene,
B. at least one C3-C20 xcex1-olefin,
C. at least one polyene, and
D. a mixed CGC system comprising a first catalyst and a second catalyst, each catalyst having substantially the same reactivity ratio and each catalyst comprising:
1. A metal complex of formula I,
ZLMXpXxe2x80x2qxe2x80x83xe2x80x83(I)
and
2. an activating cocatalyst;
with the provisos that (i) the first catalyst is different from the second catalyst, and (ii) the weight ratio of the first catalyst to the second catalyst, based on the weight of the metal M in each catalyst, is between about 90:10 and 10:90. The definition of Z, L, M, X, Xxe2x80x2, p and q are as defined above.
In both embodiments, the polymer blend may be recovered from the reaction vessel in any convenient manner.
Each CGC of the system produces an ethylene/xcex1-olefin polymer that has substantially the same molecular architecture as the ethylene/x-olefin polymer produced by the other CGC of the system, but each polymer has a different molecular weight. The reaction temperature controls the molecular weights of the copolymers. With respect to ethylene/xcex1-olefin/polyene polymer blends, the molecular architecture of a polymer produced by one CGC of the system may differ from the molecular architecture of a polymer produced by the other CGC of the system because the reactivity ratio of the polyene may be different with each CGC of the system (although the size and distribution of the ethylene runs in each polymer molecule may be substantially similar).
The polymer blend also has a rheology ratio greater than any ethylene-based polymer component of the blend prepared in a single reactor with any single component of the mixed catalyst system under similar polymerization conditions.
By xe2x80x9cmixed catalyst systemxe2x80x9d is meant that each CGC of the system is different from the other CGC. The CGCs can differ in one or more of their respective constituent parts, i.e., the metal and/or organic ligand component of the metal complex, the cocatalyst and the activator. The mixed catalyst system can comprise two or more CGCs, but dual systems (i.e., systems containing essentially only two CGCs) are preferred.